Cadmium (Cd) is an important heavy metal pollution,and NO is a bioactive molecule,which was found to participate in the reaction of plant to Cd.Leaves from tomato seedlings pretreated with 100 μmol·L-1 sodium nitroprusside (SNP,as NO donor) 1 day prior to being treated with 50 μmol·L-1 Cd for 7 days were used as materials,and chloroplasts were isolated from the leaves to study the effects of NO on the spectroscopic characteristics of chlorophyll.The results of absorption spectra of chloroplasts showed that NO alleviated the effects of Cd on absorption spectra of chloroplast by raising the relative absorbance at 436 nm,480 nm and 470 nm,which caused lower contents of carotinoid and chlorophyll.Fluorescence emission spectra of chloroplasts indicated that NO alleviated effect of Cd,and the relative absorbance at 686 nm and 734 nm decreased 17% and 10% respectively,while they decreased 33% and 23% respectively in chloroplasts treated with Cd.DCPIP analysis results showed that NO alleviated the inhibition of photosynthetic electron transport by Cd,and consequently the electron transport rate reached the same level of control.